(1) Field of the Invention
The present invention relates to a picture signal processing system including a spatio-temporal filter for converting a high quality picture information signal between interlace and sequential scanning systems through a spatio-temporal filter for removing injurious multi-dimensional higher range components caused by the scanning conversion.
(2) Description of the Prior Art
The conversion of scanning systems is frequently utilized for transmitting a wideband television picture signal through a narrower band transmission line and reproducing it with a high picture quality. In the picture signal processing system of this kind, the scanning conversion from the sequential system to the interlace system is usually effected for reducing a frequency band width required for transmitting a sequential scanning high quality picture signal accompanied with no deterioration of picture quality in the reproduction thereof. However, the reproduced interlace scanning picture has various defects such as the noticeable line structure of alternate fields and the impaired natural motion of picture cause the serious deterioration of picture quality. Particularly, the reproduced line-interlace scanning picture has an essential defect that the vertical resolution thereof is reduced to about 70% of an expectancy based on the number of lines by the above mentioned line structure. So that, regarding the high quality television, the interlace scanning picture signal, which has an advantage that the transmission band width can be reduced with the maintained flicker performance, is adopted principally into the transmission thereof. That is, the high quality sequential scanning picture signal, which has a number per second of frames increased more than the standard thereof, is intermittently sampled and expanded along the time axis, so as to be converted into the interlace scanning picture signal which can be transmitted through the narrower band transmission line.
In the above situation where the signal is sampled for the conversion of temporal frequency domain, unnecessary frequency components other than necessary frequency components generated by the conversion, including the sampling frequency component and harmonics thereof, are apt to be generated and intermixed with essential picture signal components, particularly, higher frequency range components, so that the expected high quality of the reproduced picture is seriously deteriorated as an essential problem.
For removing the above unnecessary frequency components accompanying the sampling of the picture signal, a conventional filter having a simple frequency response based on a simple one-dimensional constitution has been employed. However, particularly for removing those unnecessary frequency components from the high quality picture signal such as a high definition television signal, it is required to effect the multi-dimensional processing, for instance, two- or three-dimensional processing upon signal components appearing along horizontal and vertical frequency axes as well as along a temporal frequency axis of multi-dimensional coordinates along with the above mentioned scanning conversion including the sampling.
Moreover, the above mentioned multi-dimensional processing is required at the receiving end of the transmission line in which the converted interlace scanning picture signal is reconverted into the original sequential scanning picture signal to be displayed with the high definition, for removing unnecessary signal components generated in connection with conversion.